Submitted to: Field Crops Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/22/2016
Publication Date: 7/6/2016
Citation: Gizaw, S.A., Garland Campbell, K.A., Carter, A.H. 2016. Evaluation of agronomic traits and spectral reflectance in Pacific Northwest winter wheat under rain-fed and irrigated conditions. Field Crops Research. doi: 10.1016/j.fcr.2016.06.018. Interpretive Summary: Drought events constrain wheat production in the Pacific Northwest of the US and are expected to play an even greater role in the future. This study was undertaken to see if spectral reflectance imaging techniques could predict plant response to water deficits and to determine which specific spectral indices were correlated with winter wheat yields. Several of the spectral indices were highly correlated with yield and can be used by wheat breeders and agronomists to predict plant response to drought. This research will improve the ability of breeders to select for improved performance and potentially assist farmers to determine when their crop is suffering from drought.
Technical Abstract: The US Pacific Northwest (PNW) is a major winter wheat mega-environment characterized by a high latitude and a Mediterranean-like climate. Wheat production is predominantly rain-fed and often subject to low soil moisture. As result, discovery and introgression of drought-adaptive traits in modern cultivars has been an integral component of the regional breeding programs. The main goal of this research was to evaluate winter wheat accessions adapted to the PNW for phenotypic interrelationships and biophysical dynamics of developmental and morpho-physiological traits in a wide range of moisture regimes. A diversity panel of 402 wheat genotypes (87 hard and 315 soft) was evaluated for spectral reflectance indices (SRIs), flag leaf senescence, phenology, and grain yield under water deficit, irrigated, and moist-cool conditions in 2012 and 2013. The effects of genotype and environment were significant on all studied traits (p < 0.001). Variation in soil moisture and temperature cumulatively explained 86% of total yield variation across years and locations. Normalized difference vegetation index (NDVI), anthocyanin reflectance index (ARI), normalized chlorophyll pigment ratio index (NCPI), photochemical reflectance index (PRI), normalized water index (NWI), green normalized vegetation index (GNDVI), and simple ratio vegetation index (SR) showed consistent patterns of response to drought and strong phenotypic correlation with grain yield (p < 0.001). Stay green estimate using flag leaf senescence was strongly correlated with area under vegetation index curve (AUVIC) (p < 0.001). The total variation in stay green explained by the variation in NDVI ranged from 53 to 88%. Principal component analysis of the studied agronomic and physiological traits revealed 3 major clusters of traits that explained 76% of their overall covariance. This study highlighted the potential use of spectral radiometry in field screening of genotypes for grain yield and drought adaptation in the PNW winter wheat mega-environment.